A universal joint with improved stiffness

ABSTRACT

The universal joint (5, 7) includes first and second forks (23, 25) each having a pair of arms (61) with seats (61.1) for respective trunnions (27.1) of a spider (27). The arms (61) extend from an outer edge (91.1) of a collar (91) provided to increase the stiffness of the arms and reduce bending deformations thereof under heavy load operating conditions.

TECHNICAL FIELD

The present invention relates to the fields of power transmitting driveshafts. In particular, embodiments described herein refer to driveshafts to be used in agricultural machinery.

BACKGROUND TO THE INVENTION

Telescopic drive shafts are commonly used for transmitting power from apower source to an operating machine that can move relative to the powersource. In many applications, the power take-off of the power source andthe input shaft of the operating machine reciprocally move in such a waythat the transmission shaft has to take different angular positions.

This need is particularly significant in agriculture, where operatingmachines of different kinds are connected to a tractor that constitutesthe power source. The tractor is used to move the operating machine, aswell as to supply it with power. The power source and the operatingmachine are mechanically connected through a drive shaft.

A drive shaft is generally constituted by a telescopic shaft and two enduniversal joints. The telescopic shaft comprises an outer tubular shaft,inside which an inner shaft, usually tubular, is slidable inserted. Theouter shaft and the inner shaft, also called tubes, are torsionallycoupled together, for instance through a spline, to allow torquetransmission from one to the other. One of the end universal joints isconnected to an end of the outer shaft forming the telescopic shaft,whilst the other universal joint is connected to an opposite end of theinner shaft. One of the two universal joints is used to couple the driveshaft to the power take-off of the power source, whilst the other isused to couple the drive shaft to the power take-off of the drivenmachine. This drive shaft allows the power source and the driven machineto move relative to each other, keeping the reciprocal mechanicalconnection.

In use, due to the mutual displacements of the power source and thedriven machine, the outer shaft and the inner shaft slide with respectto each other when rotating under load.

An accident-preventing protection covers the telescopic shaft and atleast part of the end universal joints.

Lubrication systems have been developed for improving the operation ofthe telescopic shaft, which are adapted to lubricate the surfaces of theinner shaft and of the outer shaft in sliding contact with one another.WO98/58183 and U.S. Pat. Nos. 5,173,082, 6,511,379 and EP 2520813disclose lubrication systems for lubricating the inner and outer tubularshafts forming the telescopic shaft. These lubrication systems haveallowed significantly improving the telescopic shaft operationconditions. However, these lubrication systems can be further improved,especially as regards the number of required greasing interventions.

Modern telescopic shafts have splined profiles with a plurality oflongitudinal projections shaped like tabs or lobes, extendinglongitudinally according to the axis of the telescopic shaft. An exampleof this kind of splined profiles is disclosed in U.S. Pat. No.5,718,266. In these telescopic shafts, torque and power are transmittedthrough the contact between a flank of each longitudinal projection ofthe inner tubular shaft and a corresponding flank of a groove of theouter tubular shaft. In the contact area, high pressure is generated.The more elongated the telescopic shaft is, the higher the pressure is,because of the reduced axial extension of the contact surface due to theextraction of the inner shaft from the outer shaft. The pressure betweenthe mutually co-acting surfaces of the inner and outer tubular shaftsgenerates friction, and thus wear of the mechanical components, as wellas resistance against axial sliding, adversely affecting thetransmission operation.

WO98/58183 discloses a drive shaft of the type described above, providedwith an accident-preventing protection. This protection comprises atelescopic tubular protection surrounding the outer shaft and the innershaft of the drive shaft and formed by a first guard tube and a secondguard tube, inserted into the first one, that can slide with respect toeach other to follow the drive shaft shortening and lengtheningmovements. The accident-preventing protection further comprises endboots for each of the two universal joints of the drive shaft. Each endboot is fastened to the telescopic tubular protection, more precisely toone of the two guard tubes forming it, and may have a flexible hoodintegral with a rigid annular structure. The end boot is fastened to theinner fork of the respective universal joint through the rigid annularstructure. Each rigid annular structure comprises an annular slidingblock slidably engaged in an annular groove provided on the sleeve ofthe inner fork of the respective universal joint. Each end boot furthercomprises a lubrication system, adapted to lubricate with lubricatinggrease the surfaces, formed by the annular sliding block and the annulargroove, in sliding contact with one another.

The lubricating grease reduces during operation, and is partiallydispersed in the environment. To operate properly, theaccident-preventing protection therefore needs frequent greasinginterventions, requiring to shut the machine, in which the drive shaftis installed, down, and to add lubricant, typically using a greasingnipple, to keep the mutually touching and mutually sliding surfaces ofthe annular groove and the annular sliding block sufficiently greased.

In these known drive shafts, the need for frequent greasinginterventions is a drawback. It would be therefore useful andadvantageous to have available a drive shaft with respectiveaccident-preventing protection, allowing reducing the greasinginterventions.

Greasing problems arise also for the universal joints, and morespecifically for the needle bearings interposed between the spidertrunnions and the seats of the trunnions in the arms of the forks of theend universal joints. Inevitably, the lubricant grease leaks through thebearing seals, and this requires continuous refilling through greasingoperations.

Moreover, especially in agricultural applications, the universal jointsare subjected to significant dynamic stresses, due to the fact that thejoints of the drive shaft operate with a significant angular offset.Furthermore, in these applications very high torques shall betransmitted. All this results in high dynamic stresses on the bearingsof the universal joints.

It would be therefore useful and advantageous to have available driveshafts requiring fewer greasing interventions, or even no greasing ofthe joints. It would be also advantageous to optimize the operatingconditions of the joints under load.

In general, it would be therefore advantageous to have available a driveshaft which completely or partially overcomes at least some of thedrawbacks of the prior art drive shafts, above all as regards greasingrequirements and useful life of the wearable components.

SUMMARY

To overcome, at least partially, the drawbacks of the prior art driveshafts, a device according to claim 1 is suggested.

Particularly advantageous embodiments are defined in the dependentclaims.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood by following the descriptionbelow and the attached drawing, showing a non-limiting embodiment of theinvention. More specifically, in the drawing:

FIG. 1 shows a cross-section of a drive shaft according to a planecontaining the shaft axis;

FIG. 2 shows a cross-section according to the line II-II of FIG. 1 ;

FIG. 3 shows an enlargement of a first end of the drive shaft of FIG. 1;

FIG. 4 shows an enlargement of the other end of the drive shaft of FIG.1 ;

FIG. 4A shows an enlarged cross-section of the detail indicated by theletter A in FIG. 4 ;

FIG. 5 is an enlarged and partially cut-away isometric view of the endof FIG. 3 of the drive shaft;

FIG. 6 is an enlarged and partially cut-away isometric view of the endof FIG. 4 of the drive shaft;

FIG. 7 shows the end of the drive shaft illustrated in FIG. 5 , withsome parts removed;

FIG. 8 shows the end of the drive shaft illustrated in FIG. 6 with someparts removed;

FIG. 9 is a cut-away isometric view of the inner shaft with thelubricating system of the telescopic shaft;

FIG. 10 is a view according to X-X of FIG. 9 ;

FIGS. 11 and 12 are isometric views, according to two different angles,of the lubricant distribution block of the system of FIG. 9 ;

FIG. 13 is a front view according to XIII-XIII of FIG. 12 .

FIG. 14 is a cross-section according to the line XIV-XIV of FIG. 13 ;

FIG. 15 shows a cross-section according to XV-XV of FIG. 14 ;

FIGS. 16 and 17 are isometric views, according to two different angles,of the block where the lubricant receiving chamber of the lubricationsystem of FIG. 9 is realized;

FIG. 18 shows a cross-section according to XVIII-XVIII of FIG. 17 ;

FIG. 19 shows a cross-section according to XIX-XIX of FIG. 18 ;

FIG. 20 is a side view of one of the inner forks of the universal jointsof the drive shaft of FIG. 1 ;

FIG. 21 shows a cross-section according to the plane with trace XXI-XXIof FIG. 22 of the inner fork of FIG. 20 ;

FIG. 22 shows a cross-section according to a plane with trace XXII-XXIIof FIGS. 20 and 21 ;

FIG. 23 is a side view, analogous to that of FIG. 20 , of one of theouter forks of the universal joints of the drive shaft of FIG. 1 ;

FIG. 24 shows a cross-section according to a plane with trace XXIV-XXIVof FIG. 25 ;

FIG. 25 shows a cross-section according to the plane with trace XXV-XXVof FIGS. 23 and 24 ;

FIG. 26 shows a cross-section of one of the spiders of the universaljoints of the shaft of FIG. 1 according to a plain containing the axesof the four trunnions of the spider, according to t plane with traceXXVI-XXVI of FIG. 27 ;

FIG. 27 shows a cross-section according to a plane with traceXXVII-XXVII of FIG. 26 ;

FIG. 28 shows an enlargement of a bearing of the spider of FIGS. 26 and27 ; and

FIGS. 29 and 30 show cross-sections of the inner shaft and the outershaft, respectively, of the drive shaft of FIG. 1 .

DETAILED DESCRIPTION

In the following description and the attached claims, the term“approximately” indicates a quantity that is approximate, with anapproximation of +/−15%, preferably +/−10% and in some instancespreferably +/−5%. In other words, “approximately A” refers to aninterval comprised between (A+0,15A) and (A−0,15A), and preferablybetween (A+0,1A) and (A−0,1A), or between (A+0,05A) and (A−0, 05A).

FIG. 1 shows a cross-section, according to a longitudinal planecontaining the rotation axis, of a drive shaft 1; FIGS. 2 to 8 showenlargements of the two ends of the drive shaft 1, in some cases withcut-away and/or removed parts.

With reference to FIGS. 1 to 9 , the drive shaft 1 generally comprises apower transmitting telescopic shaft 3 with two ends; with these ends, afirst universal joint 5 and a second universal joint 7 are associated.As better detailed below, the universal joints 5 and 7 have connectionmeans for connecting to power take-offs of the power source and of theload, i.e. a driven machine for instance.

The telescopic shaft 3 comprises two tubular elements, simply called“telescopic tubes”, one of which is inserted inside the other. More inparticular, in the embodiment of FIG. 1 the telescopic shaft 3 comprisesa first tubular element, here below referred to as outer tubular shaftor simply outer shaft 9, and a second element, that is tubular in theillustrated example, referred to as inner tubular shaft or simply innershaft 11.

The inner shaft 11 is inserted in the outer shaft 9 in telescopicfashion, and both are so shaped as to slide with respect to each otherparallel to the axis A-A of the telescopic shaft; however, therespective cross-sections of the shafts are such that the shafts cannotrotate with respect to each other. This means that the shafts aretorsionally coupled together so as to rotate integrally and to transmitpower from a power source (not shown) to a user, i.e. a load,constituted for example by a driven machine or an operating machine (notshown).

As shown in particular in the cross-section of FIG. 2 , the shafts 9 and11 have a non-circular tubular wall, so as to torsionally coupletogether. More in particular, the shape of the cross-section of both theshafts 9 and 11 has four longitudinal projections, through which the twotubular shafts 9 and 11 engage. Specifically, the inner shaft 11 hasfour longitudinal projections 11.1, engaging inside grooves provided atas many longitudinal projections 9.1 of the outer shaft 9. More detailson the configurations of the shafts 9 and 11 will be described below.

The universal joint 5 is connected to an end of the inner shaft 11 andcomprises a first fork 23 and a second fork 25, joined together by meansof a spider 27. Here below, the fork 23 will be also called inner fork,whilst the fork 25 will be called outer fork. The inner fork 23 isrigidly connected to the first end of the inner shaft 11 of thetelescopic shaft 3, whilst the outer fork 25 may be connected to a powertake-off or to any other member of a mechanical transmission line, notshown, of which the drive shaft 1 is part.

Analogously to the universal joint 5, also the universal joint 7comprises a first fork (inner fork), indicated again with referencenumber 23, and a second fork (outer fork) indicated again with referencenumber 25, joined together by means of a spider indicated again withreference number 27. The inner fork 23 is rigidly connected to a firstend of the outer shaft 9, whilst the outer fork 25 may be connected to apower take-off or to any other member of a mechanical transmission line,not shown.

The drive shaft 1 also comprises an accident-preventing protection 13.The accident-preventing protection 13 comprises a telescopic tubularprotection formed by a pair of tubular elements 15, 17, one of which isslidable inserted in the other. The tubular elements 15, 17 (here belowreferred to simply as “tubes”) are preferably so shaped as to betorsionally coupled, i.e. they cannot rotate with respect to each otheraround the axis A-A of the telescopic shaft 3, but they can axiallyslide in the direction of the axis A-A. In this way, theaccident-preventing protection 13 can follow the lengthening andshortening movements of the drive shaft 1. The shape of thecross-section of the tubes 15, 17 is visible in FIG. 2 . The tubes 15,17 have a non-circular cross-section, for preventing the mutual rotationthereof. More in particular, in the illustrated example the two tubes15, 17 of the accident-preventing protection 13 comprise projections15.1 and 17.1, the ones inserted into the others and sliding withrespect to one another in the direction of the axis A-A.

In addition to the tubes 15 and 17, the accident-preventing protection13 further comprises two ends protections 19, one of which is associatedwith the universal joint 5 and the other with the universal joint 7.More details on the configurations of the end protections 19 will bedescribed below.

In the illustrated embodiment, the telescopic shaft 3 is provided with alubrication system 37 housed inside the inner tubular shaft 11. FIGS. 9to 19 show the components of the lubrication system in detail. Thelubrication system 37 is adapted to supply lubricant, in particularlubricating grease, in the gap between the inner shaft 11 and the outershaft 9 forming the telescopic shaft 3.

For the sake of clarity of representation, in FIG. 9 the lubricationsystem 37 and the inner shaft 11 are shown separately from the othercomponents of the drive shaft 1. The two main components of thelubrication system 37 are shown, in different views and cross-sections,in FIGS. 11 to 15 and 16 to 19 respectively.

In the illustrated embodiment, the lubrication system 37 comprises alubricant receiving chamber 39, formed in a block 39.1, and a lubricantdistribution block 41. The block 39.1 is shown in detail in FIGS. 11 to15 , whilst the lubricant distribution block 41 is shown in FIGS. 16 to19 .

In the illustrated embodiment, the block 39.1 is fastened in the hollowspace of the inner shaft 11. For fastening, a nipple 39.3 can be forexample used, transversally extending through the wall of the innershaft 11 and through the wall of the outer shaft 9, so as to beaccessible by the operator. The nipple 39.3 can be accessed from theoutside of the accident-preventing protection through an opening 40closed by means of a protective lid 40.1, see FIG. 3 .

The lubricant receiving chamber 39 is connected to the lubricantdistribution block 41 through a delivery system 43. In the illustratedexample, the delivery system 43 comprises two transferring ducts 43.1and 43.2, for example in the form of two rigid or flexible small tubesextending in axial direction inside the inner shaft 11. Between thelubricant receiving chamber 39 and each of the transferring ducts 43.1,43.2, a gauged hole 39.2 is provided, i.e. a hole of dimensionssignificantly lower than the cross-section of the transferring duct43.1, 43.2. In this way, by injecting pressurized lubricating greaseinto the lubricant receiving chamber 39, the lubricant is supplied tothe two transferring ducts 43.1, 43.2 in balanced way, without followinga preferred path, thanks to the fact that most of the pressure drop inthe fluid system represented by the lubricating grease is concentratedin correspondence of the necking represented by the gauged holes 39.2.

Each transferring duct 43.1 and 43.2 is fastened to the block 39.1 byinserting a first end of each transferring duct 43.1, 43.2 into a seatprovided in a corresponding connection 39.4 and 39.5 of the block 39.1.The opposite end of each transferring duct 43.1, 43.2 is inserted into aseat provided in a corresponding connection 41.1, 41.2 of the lubricantdistribution block 41. The two connections 41.1 and 41.2 form tworetaining appendices of the lubricant distribution block 41 inside theinner hollow shaft 11. More in particular, the retaining appendicesengage inside two opposite grooves of the shaped profile forming theinner shaft 11, these grooves forming, on the outer surface of the innershaft 11, the longitudinal projections 11.1.

Advantageously, as shown in particular in FIGS. 9 and 16 to 19 , thelubricant distribution block 41 comprises two further retainingappendices 41.3 and 41.4, engaging the other two opposite grooves of theshaped profile forming the inner shaft 11.

In the inside thereof, the lubricant distribution block 41 comprises aplurality of lubricating ducts 41.5, 41.6, the number of which is equalto the number of transferring ducts 43.1, 43.2. In the illustratedexample, the two shafts 9, 11 have four longitudinal projections andfour respective longitudinal grooves for mutual torsional couplingtherebetween. In this case, the number of lubricant transferring ducts43.1, 43.2 and the number of lubricating ducts 41.5, 41.6 is equal tohalf the number of longitudinal grooves. Using the same ratio, if theinner and outer shafts have six longitudinal projections and sixcorresponding longitudinal grooves for torsional coupling, threelubricating ducts and three corresponding lubricant transferring ductsmay be provided.

Each lubricating duct 41.5, 41.6 is fluidly connected to lubricantsupply ports, so arranged as to supply lubricant in the gap between theouter shaft 9 and the inner shaft 11 in correspondence of thelongitudinal projections 9.1 and 11.1, i.e. near the mutually touchingand mutually sliding surfaces of the shafts 9, 11.

In the illustrated embodiment, each lubricating duct 41.5 and 41.6 isfluidly connected to two respective transverse holes 41.7, 41.8 and41.9, 41.10 respectively. The transverse holes 41.7 and 41.9 end incorrespondence of the appendices where the ends of the transferringducts engage, whilst the transverse holes 41.8 and 41.10 end on theouter surfaces of the retaining appendices 41.3 and 41.4. The transverseholes 41.7 and 41.8 fluidly connected to the lubricating duct 41.5 andto the lubricant transferring duct 43.1 are therefore offset withrespect to each other in a longitudinal direction, i.e. parallel to theaxis A-A of the telescopic shaft 3, and are also angularly offset, so asto supply lubricant to two longitudinal projections 11.1, arranged onefollowing the other in two different positions along the axial extensionof the telescopic shaft 3. Analogously, the transverse holes 41.9 and41.10 are offset both in axial direction and angularly, and are soarranged as to supply lubricant to the two remaining longitudinalprojections 11.1.

The inner shaft 11 has four radial holes, on the four longitudinalprojections 11.1, aligned with the transverse holes 41.7, 41.8, 41.9 and41.10. More in particular, the four radial holes are provided on thehead surfaces of the longitudinal projections 11.1, i.e. on theoutermost radial surfaces of the inner shaft 11. For the sake ofaccuracy, the lubricant distribution block 41 may be manufactured devoidof the holes 41.7, 41.8, 41.9 and 41.10, these latter being machinedonce the lubricant distribution block 41 has been inserted into theinner shaft 11. Both the radial holes in the head surfaces of thelongitudinal projections 11.1 of the shaft 11, and the transverse holes41.7, 41.8, 41.9, 41.10 in the lubricant distribution block 41 can bemachined with a drilling tool.

As the wall of the inner shaft 11 shall have through holes incorrespondence of the transverse holes 41.7, 41.8, 41.9, 41.10, thearrangement described above with the holes in axially offset positionsprevents excessive weakening of a cross-section of the inner shaft 11.

To connect directly the lubricating ducts 41.5, 41.6 and the gapsbetween the inner shaft 11 and the outer shaft 9, tubular pins 51 may beprovided, extending from the respective lubricating duct 41.5, 41.6 upto the head surface of the respective projections 11.1 of the innershaft 11 through holes 11.9 of the tubular wall of the inner shaft 11that define lubricant supply ports. The tubular pins 51 are also used tohold the lubricant distribution block 41 in a correct position insidethe inner shaft 11.

With the arrangement described above, the lubricating grease can besupplied in a particularly efficient manner in the gap between the innershaft 11 and the outer shaft 9 of the telescopic shaft 3. In fact, thelubricant is supplied exactly to the areas where it is required, i.e.between the outer surfaces of the longitudinal projections 11.1 of theinner shaft 11 and the inner surfaces of the corresponding grooves ofthe outer shaft 9, where the longitudinal projections 11.1 are slidablehoused.

Furthermore, at least one lubricant supply port 11.9 is provided foreach longitudinal projection 11.1 and the lubricant supply ports arearranged longitudinally offset along the axial extension of thetelescopic shaft 3, so that the lubricant is supplied on a greaterlength of the telescopic shaft.

In order that the drive shaft 1 operates more effectively and for alonger time, in some embodiments an improved support and lubricationsystem of the accident-preventing protection 13 is provided on the innercomponents of the drive shaft 1, and more precisely on the inner forks23 of the end universal joints 5, 7.

One of the two inner forks 23 is individually illustrated in detail inthe side view of FIG. 20 and in the two cross-sections of FIGS. 21 and22 . The fork 23 comprises two arms 61, to which the spider 27 connects,and a sleeve 63; in the inner axial cavity 63.1 of the sleeve, an end ofthe outer shaft 9 or of the inner shaft 11 is inserted. The shaft isfastened to the fork by means of an axial constraint member,constituted, in the illustrated example, by a transverse pin 64 (seeFIGS. 1 and 3 ) extending across the shaft 9 or 11 and the sleeve 63through radial holes 63.2.

The inner axial cavity 63.1 is advantageously provided with a closinglid preventing solid and liquid debris from entering from the outsideduring operation of the drive shaft 1. This is particularly useful inthe agricultural industry, where the universal joint operates inenvironments where there is debris that can penetrate the telescopicshaft 3, jeopardizing the operation thereof or, anyway, making theoperating conditions of the telescopic shaft 3 worse. The presence oflids 63.5 at both ends of the drive shaft, and thus at both inner forks23 of the joints 5, 7, reduces the quantity of debris entering thetelescopic shaft 3, and protects therefore the surfaces of the tubularshafts 9, 11 in sliding contact with one another, increasing the usefullife of the telescopic shaft and reducing the need for addinglubricating grease. In this way, the telescopic shaft 3 can be greasedless frequently.

To allow the tubular shafts 9, 11 to slide freely without the formationof over- or de-pressurization therein, notwithstanding the lids 63.5closing the ends, it is sufficient to provide small air outlets,arranged in the most suitable places, for instance on the sleeve of thefork or on the lid.

The sleeve 63 has, on the outer surface thereof, an annular groove 63.3and an annular or cylindrical bearing surface 63.4, which forms anannular bearing track for the respective end protection 19, as explainedbelow.

As shown in particular in the enlarged cross-sections of FIGS. 3 and 4and in the partially cut-away isometric views of FIGS. 5 to 8 , each endprotection 19 comprises two main parts, and more precisely a flexiblehood 65 and a rigid annular structure 67. In this description, the terms“rigid” and “flexible” have a relative meaning, i.e. the hood 65 is moreflexible than the annular structure 67. In fact, the hood 65 is able tobe deformed to adapt to the mutual inclination of the two forks 23, 25of the universal joint 5, 7, whilst the annular structure 67 stablyconnects the end protection 19 and the whole accident-preventingprotection 13 to the telescopic shaft 3.

In some embodiments, the flexible hood 65 has corrugated structure andis flared, as shown in the cross-sections of FIGS. 3 and 4 . The shapeof the hood 65 is given just by way of non-limiting example. Othershapes are also possible, for example with greater or lower axialextension. The hoods 65 can be also realized in more parts combined withone another.

The annular structure 67 comprises an annular sliding block 69 engagingthe annular groove 63.3 of the sleeve 63 of the respective inner fork23. In some embodiments, the annular sliding block 69 is made of aplurality of parts, for example two separate semi-annular parts, forinstallation easiness. In use, the annular sliding block 69 isstationary, as it is integral with the accident-preventing protection13, whilst the drive shaft 1 rotates inside the accident-preventingprotection 13. The annular sliding block 69 and the annular groove 63.3form a first coupling between the accident-preventing protection 13 andthe drive shaft 1. In addition to act as radial support between the endprotection 19 and the inner fork 23, the coupling between the annulargroove 63.3 and the annular sliding block 69 also acts as an axialcoupling, fastening the end protection 19 to the inner fork 23 of therespective universal joint 5, 7 in the direction of the axis A-A of thetelescopic shaft 3. As each end protection 19 is rigidly connected toone of the two tubes 15, 17, this axial coupling constrains the wholeaccident-preventing protection in axial direction with respect to thetelescopic shaft 5 and the universal joints 5, 7.

In the illustrated embodiments, the annular structure 67 comprises asliding ring 71 and a containment sleeve 73, torsionally and axiallycoupled together, i.e. so coupled as to be prevented from moving withrespect to each other in the direction of the axis A-A of the telescopicshaft 3, and angularly around this axis.

The sliding ring 71 has a flange 71.1 and a tubular portion 71.2surrounding the sleeve 63 of the respective fork 23 of the universaljoint 5 or 7. The containment sleeve 73 has a flange 73.1 and a tubularportion 73.2 externally surrounding the tubular portion 71.2 of thesliding ring 71. The tubular portion 73.2 has a plurality of annulartabs 73.3, for purposes that will be described below. The two flanges71.1 and 73.1 are joined together by means of joining elements, forexample screws 75. The mutual angular position of the flanges 71.1 and73.1 can be defined through reference pins 76 that are integral with theflange 71.1 and enter in holes of the flange 73.1, or vice versa.Between the two flanges 71.1 and 73.1, an inwards facing annular edge65.1 of the hood 65 is locked. In this way, the hood 65 of the endprotection 19 is fastened to the annular structure 67.

The annular sliding block 69, and more exactly the two or more portionsforming it, are kept in a seat formed by the tubular portion 73.2 of thecontainment sleeve 73 and by the sliding ring 71. Appendices 69.1 of theportions forming the annular sliding block 69 torsionally couple theannular sliding block 69 to the sliding ring 71, so that the annularsliding block 69 does not rotate with respect to the annular structure67.

The inner surface of the sliding ring 71 forms a rest on the annulartrack 63.4. As shown in particular in FIGS. 3 and 4 , between theannular sliding block 69 and the annular track 63.4 a space is defined,delimited by the annular sliding block 69 and the annular track 63.4, aswell as by the outer surface of the sleeve 63 of the inner fork 23, andby the sliding ring 71. This space forms a lubricating grease reservoir,to grease the rest and mutual sliding surfaces between the inner fork 23and the end protection 19. The rest and sliding surfaces are representedby the annular groove 63.3 and by the respective annular sliding block69, as well as by the annular track 63.4 and by the inner surface of thesliding ring 71. These two rest surfaces are spaced from each other inaxial direction, as therebetween there is interposed the axialconstraint member (pin 64) fastening the inner fork 23 to the outershaft 9 or to the inner shaft 11 of the telescopic shaft 3. Thisdistance allows to optimize support and to form a relatively capaciousspace for the lubricating grease.

The lubricating grease reservoir defined between the sliding ring 71 andthe containment sleeve 73 may be filled with lubricating grease forinstance through at least one nipple 81 which may be integral with thecontainment sleeve 73, or made in a single piece therewith. The annulartabs 73.3 may protect the nipple 81 from impacts against external items,especially when transporting the drive shaft 1.

The arrangement described above allows to have available a significantquantity of lubricating grease inside the accident-preventing protection13, and especially in the area of sliding contact between the endprotections 19 and the inner forks 23 of the universal joints 5, 7. Thisallows the drive shaft to have a long life without the need forintermediate greasing interventions.

Moreover, the space containing the lubricating grease has an annularextension and forms a barrier efficiently contributing to avoid, or tolimit, liquid and solid debris entering towards the inside of thetelescopic shaft 3. This increases the useful life of the telescopicshaft 3 and reduces the needs for greasing it.

In order efficiently to couple each end protection 19 to the telescopictubular protection formed by the tubes 15, 17, nut and bolt couplingsystems may be provided. For example, a bolt 83 may be provided, as wellas a tubular nut 85 with an internally threaded hole and a hexagonalhead, see in particular FIGS. 3 and 4 and the enlarged cross-section ofFIG. 4A. Advantageously, the length of the tubular nut 85 may be such asto extend through almost the entire thickness of the respective tube 15or 17 and of the tubular portion 73.2 of the containment sleeve 73. Inthis way, the two screw members are coupled together, and thecontainment sleeve 73 and/or the tube 15 or 17 are pressed in acontrolled manner. In this way, the components 15, 17, 73, usually madeof plastic, of the accident-preventing protection are not damaged due tocompression. An elastic ring 87 prevents the two screw members 83, 85from unscrewing. The elastic ring 87 also acts as a support for the headof the bolt 83, which therefore does not directly press against, norrub, the plastic material, of which the accident-preventing protection73 is made. Even if in the drawing only a single nut and bolt system 83,85, 87 is shown, in advantageous embodiments these coupling elements maybe more, for example two, three or four, uniformly distributed aroundthe axis A-A of the drive shaft.

In order to improve the operating conditions of the universal joints 5,7 and the overall efficiency of the drive shaft 1, in some embodimentsdescribed herein a particular shape for the inner forks 23 and the outerforks 25 of the universal joints 5, 7 is provided. One of the innerforks 23 is shown in detail in FIGS. 20, 21, 22 , and one of the outerforks 25 is shown in detail in FIGS. 23, 24 and 25 .

As mentioned above, the inner forks 23 comprise a sleeve 63, internallyperforated and grooved for being inserted into, and torsionally coupledto, the end of the outer shaft 9 or of the inner shaft 11, the end beingfastened to the inner fork 23 through an axial constraint member, in theillustrated example constituted by the pin 64 (FIG. 3 ). From the sleeve63 a collar 91 extends, ending with an end edge 91.1, in particular andadvantageously of circular shape, opposite the sleeve 63. The arms 61 ofthe inner fork 23 extend from the end edge 91.1. In the illustratedembodiment, the sleeve 63, the collar 91 and the arms 61 are made in asingle piece, for example by casting and subsequent chip removalmachining.

In the illustrated embodiment, the collar 91 has a toroidal hollowshape, essentially a cup-shape, surrounding a concave inner space. Theconcave inner space is delimited by a surface, shaped approximately as aspherical zone, defined between a plane tangent to the edge 91.1 and bya plane orthogonal to the axis A-A of the fork 23 (coinciding with theaxis A-A of the telescopic shaft 3) and passing through the end of theaxial cavity 63.1 of the sleeve 63.

The concave inner space delimited by the collar 91 has a height H in thedirection of the axis A-A of the fork. The height H is essentially theheight of the spherical segment delimited by the plane tangent to theedge 91.1 and by the plane passing through the end of the inner axialcavity 63.1.

The letter L indicates the length of the arms 61 of the fork 23. Thecollar 91 allows reducing the length of the arms 61 and increases thebending stiffness of the arms 61.

Advantageously, the height H of the concave space inside the collar 91is at least approximately 10% of the length L of the arms 61. The heightH is preferably equal to, or greater than, approximately 15%, morepreferably equal to, or greater than, approximately 20% of the length L,and not greater than approximately 50%, preferably not greater thanapproximately 40% and more preferably not greater than approximately 30%of the length L of the arms 61.

Each arm 61 comprises a seat 61.1 with circular cross-section, where oneof the four trunnions 27.1 that extend from a central body 27.4 of thespider 27 (FIGS. 26, 27 ) are housed. Between each trunnion 27.1 and therespective seat 61.1, a radial needle bearing 95 is positioned,described below in greater detail (see FIGS. 26, 27, and 28 ).Practically, each needle bearing 95 is mounted stably on the respectivetrunnion 27.1 of the spider 27.

Each seat 61.1 has a diameter D. For a more advantageous operation, aswill be better explained below, the ratio between the diameter D and thedistance C of the center of the seat 61.1 from the edge 91.1 of thecollar 91 is comprised between approximately 0.7 and approximately 1.1,and preferably comprised between approximately 0.7 and approximately0.95. Due to the fact that, for the reasons explained below, it ispreferable that the diameter of the trunnions 27.1 of the spider 27 begreater than that of the trunnions of the prior art joints, in preferredembodiment the ratio mentioned above is equal to, or greater than,approximately 0.75, and equal to, or lower than, approximately 1.1,preferably not greater than approximately 1.

In some embodiments, the center of curvature of the spherical innerconcave surface of the collar 91 is located on the axis (B-B) of therespective aligned pair of seats 61.1 of the respective pair of arms 61.In some embodiments, the ratio between the diameter D of each seat 61.1)and the radius of the inner concave surface of the collar is comprisedbetween about 0.48 and about 0.65, preferably between about 0.49 andabout 0.64.

The structure and ratios indicated above are characteristic of the forkfor a reduced length of the arms 61. However, the seats 61.1 provided insaid arms 61 are adequately spaced from the sleeve 63 thanks to thepresence of the collar 91. The flared or cup-like shape of the collar 91allows an appropriate maximum mutual inclination of the axes of theinner and outer forks 23, 25 of the joints 5, 7. Practically, thedimensions are such that the axes of the two forks 23, 25 of the sameuniversal joint 5, 7 can take any mutual angular position, from thecoaxial position (angle between the axes equal to 0°) up to a positionof maximum inclination (angle between the axes equal to approximately75°, for instance).

As shown in FIGS. 26, 27 , and in particular in the enlargement of FIG.28 , each needle bearing 95 comprises a cylindrical cup-shaped housing95.1. The cylindrical housing 95.1 comprises a cylindrical wall with aninner cylindrical surface 95.2, and a substantially flat bottom surface95.3 orthogonal to the axis of the needle bearing 95. Each needlebearing 95 comprises a plurality of needles 95.4 provided between thecylindrical surface of the respective trunnion 27.1 and the innercylindrical surface 95.2 coaxial to the trunnion 27.1. Thanks to theincreased diameter of the seats 61.1 and, therefore, of the needlebearings 95, it is possible to house, in each needle bearing 95, arelatively high number of needles 95.4, greater than that provided forin the prior art universal joints.

On the side opposite the bottom surface 95.3, the housing 95.1 is closedby means of a lip seal 95.6 housed in a containment ring 95.5, to avoid,or to reduce, the leakage of lubricating grease contained in the needlebearing 95.

Advantageously, the bottom surface 95.3 of the cylindrical housing 95.1is spaced from the end surface of the respective trunnion 27.1. To thisend, an annular spacer 95.7 may be provided, for instance. The distanceE between the end surface of the trunnion 27.1 and the bottom surface95.3 of the cylindrical housing 95.1, i.e. the thickness of the annularspacer 95.7, is at least equal to the radius of the needles 95.4 andequal to, or lower than, three times the radius. The annular spacer 95.7may be made of a material different from that of the spider 27 and thehousing 95.1. For example, these latter may be made of metal, and theannular spacer 95.7 may be made of a polymeric material. The annularspacer 95.7 reduces, or eliminates, the axial clearance between eachhousing 95.1 and the respective trunnion 27.1 of the spider 27.

In advantageous embodiments, the spider 27 have an inner channelextending along the spider arms, on which the trunnions 27.1 areprovided. The inner channel may be constituted by two orthogonal holes27.2 coaxial with the axes of the trunnions 27.1 of the spider 27. Thethrough holes end on the end surfaces of the four trunnions 27.1 of thespider 27.

As mentioned above, given the same torque that can be transmitted by theuniversal joint, of which the spider 27 is part, the trunnions 27.1 ofthe spider 27 have larger diameter than the trunnions of the prior artspiders. This allows providing holes 27.2 of relatively large diameter,thanks both to the greater space available inside the trunnions, and tothe fact that the trunnions 27.1, having larger diameter than that inthe prior art spiders, can be made hollow, while keeping a sufficientmechanical strength for transmitting forces.

In advantageous embodiments, the ratio between the maximal innerdiameter (indicated with D2 in FIG. 28 ) of the hole 27.2 along therespective trunnion 27.1 and the outer diameter (indicated with D1 inFIG. 28 ) of the trunnion 27.1 is equal to, or greater than,approximately 0.3, preferably equal to, or greater than, approximately0.4, more preferably equal to, or greater than, approximately 0.6. Inpreferred embodiments disclosed herein, the ratio is not greater thanapproximately 0.8, preferably not greater than approximately 0.75. Inadvantageous embodiments, the ratio D2/D1 is comprised betweenapproximately 0.4 and approximately 0.7.

The set of holes 27.2 forms a lubricating grease reservoir, fluidlyconnected to the needle bearings 95 through the space between the headof the trunnions 27.1 and the bottom surface 95.3 of the housings 95.1,where the annular spacer 95.7 is provided. In this way, when filling thespace of the holes 27.2 with lubricating grease, a stock of lubricatinggrease is formed, that can be enough to ensure lubrication for the wholeuseful life of the universal joint 5, 7, of which the spider 27 is part.This is obtained thanks to the large diameter of the holes 27.2 andtherefore thanks to the large space available for storing lubricatinggrease.

In use, the rotation of the universal joint 23, 25, of which the spider27 is part, generates, due to the centrifugal force, a thrust on thelubricating grease that is pushed towards the ends of the trunnions27.1, and therefore towards the needle bearings 95.

The channel system formed by the holes 27.2 may be fluidly coupled tothe environment through a valve 27.3 that can be arranged, for exampleand preferably, in the center of the spider (see FIG. 27 ). The valve27.3 is a check valve, so mounted as to allow air to enter in thechannel system formed by the holes 27.2 and to prevent lubricatinggrease from leaking from the inside of the spider 27. Through the valve27.3, air can gradually enter the space formed by the holes 27.2, so asto fill the space left free by the lubricating grease that inevitablyleaks through the seals 95.6. Therefore, the valve 27.3 avoidsdepressurization inside the spider 27; the depressurization wouldotherwise prevent or hinder the flow of the lubricating grease from theholes 27.2 towards the needle bearings 95.

The axial length of the needles 95.4 of the needle bearings 95 isindicated with F in FIG. 28 . Advantageously, having a number of needles95.4 greater than in the prior art universal joints, thanks to thelarger diameter of the trunnions 27.1 of the spiders 27, it is possibleto reduce the axial length F of the needles without reducing the overallsurface of contact between needles 95.4 and trunnion 27.1, i.e. the sumof the surfaces of contact between each needle 95.4 a the trunnion 27.1of a single needle bearing 95.

In advantageous embodiments, the ratio between the length F (expressedin millimeters) of each needle 95.4 and the number of needles 95.4 in aneedle bearing 95 is equal to, or lower than, approximately 0.39,preferably equal to, or lower than, approximately 0.36, in someembodiments equal to or lower than approximately 0.32. Preferably, thisratio is equal to, or greater than, approximately 0.18, in particularand preferably equal to, or greater than, approximately 0.21. Thesevalues are essentially lower than those provided for in the prior artuniversal joints, and are indicative of a different mode of distributingthe load between trunnion 27.1 of the spider 27 and needles 95.4 of theneedle bearing 95. Practically, reversely to what it is usually providedfor, the axial length of the needles 95.4 decreases and the overallsurface of contact between needles 95.4 and trunnion 27.1 of the spider27 increases by increasing the number of needles 95.4 of the singleneedle bearing 95, thanks to an increase in the diameter of thetrunnions 27.1 of the spider 27.

A larger number of needles 95.4 arranged in each needle bearing 95implies a larger diameter of the respective trunnion and/or a reductionof the diameter of the needles. Increasing the diameter of the trunnion27.1 of the spider 27 is beneficial not only because it allows a largernumber of needles to be arranged in each needle bearing, but alsobecause it allows a larger grease reservoir to be provided inside thespider 27. In implementations, the dimensions of the needles and of thetrunnion are selected such that the ratio between the length of theneedles 95.4 of each needle bearing 95 and the diameter of therespective trunnion 27.1 is lower than approximately 0.56, preferablylower than approximately 0.5, preferably lower than approximately 0.45,more preferably equal to, or lower than, approximately 0.42. In someembodiments, the needles 95.4 have a diameter comprised betweenapproximately 2.2 and approximately 3.2 mm, preferably betweenapproximately 2.5 and approximately 3 mm.

It has been surprisingly found that this different approach indimensioning the needles 95.4 have great advantages in terms ofoperation and useful life of the universal joint 5, 7. In fact, it hasbeen experimentally found that the shorter needles 95.4 tend better tokeep the parallelism between axis of the needles 95.4 and axis of therespective trunnion 27.1. In this way, even when the universal joint 5,7 is strongly loaded and operates with misaligned forks 23, 25, theneedles 95.4 tend less to be arranged with the axis inclined withrespect to the trunnion axis. This ensures that, under any operatingconditions, the needles 95.4 are correctly in contact, for the wholeaxial length thereof, both with the outer cylindrical surface of therespective trunnion 27.1, and with the inner cylindrical surface 95.2 ofthe housing 95.1. This optimizes the exploitation of the length of thesingle needles and avoids anomalous wear concentration in the needlesliding tracks formed by the housing 95.1 and by the trunnion 27.1 ofthe spider 27.

The different dimensioning of the components of the needle bearings 95described above may have a synergistic effect with the increased bendingstiffness of the arms 61 of the fork 23 achieved through the collar 91described above. This allows the universal joint 5, 7 to better operateunder any load conditions and with any angles between the axes of theforks 23, 25 thanks to the combination of two effects: reduction in thebending deformation of the arms 61 of the forks 23, 25, and betterkinematic behavior of the needle bearings 95.

The lubricating grease reservoir formed in each spider and behind eachneedle bearing 95, between the head surface of the trunnion 27.1 and thebottom surface 95.3 of the housing 95.1, ensures better and more durablegreasing.

As a result of the solutions described herein, the universal joint 5, 7is more durable and requires less, or even no, greasing interventions,as the duration of the lubricant is equal to the useful life of themechanical components, thanks to the stock of lubricating grease and thebetter dynamic and kinematic behavior of the joint components.

The features described above with reference to FIGS. 20, 21 and 22 forthe inner fork 23 are advantageously provided also for the outer fork 25of each universal joint 5, 7. FIGS. 23, 24, and 25 show the same viewsand cross-sections of FIGS. 20, 21 , and 22, for an outer fork 25. Thesame reference numbers indicate the same or equivalent parts in the twoforks. The torsional coupling profile between the fork 23, 25 and theshaft, with which it is integral, is different for the outer fork 25 andfor the inner fork 23, as the outer fork 25 is so shaped as to couple toa standard grooved profile, whilst the inner fork 23 is so shaped as tocouple to the inner tubular shaft 11 or to the outer tubular shaft 9 ofthe telescopic shaft 3. The remaining structural features of the outerfork 25 are substantially equal to those of the inner fork 23.Therefore, the outer fork 25 will be not described.

Further improvements to a telescopic shaft 3 and to the drive shaft 1comprising it may be achieved by using a novel profile for the two innerand outer shafts 11, 9 forming the telescopic shaft 3. Novel features ofthis component of the drive shaft 1 will be disclosed below withspecific reference to FIGS. 1, 29, and 30 .

With specific reference to FIG. 29 , the inner shaft 11 has a tubularstructure of non-circular cross-section, so as to couple torsionally tothe outer shaft 9, this latter also having a tubular structure and atransverse cross-section complementary to that of the inner shaft 11. Asindicated above, the inner shaft 11 has a tubular wall of thickness S11,defining four longitudinal projections 11.1. The four longitudinalprojections 11.1 may be at the same distance from one another or not, asin the illustrated example, so as to define a mutual coupling anglebetween the two shafts 9 and 11. Each longitudinal projection 11.1comprises a head surface 11.3 and two side flanks 11.4 joining therespective head surface 11.3 and the bottom of longitudinal grooves11.5, interposed between pairs of adjacent longitudinal projections11.1. The letter G indicates the dimension, in cross-section, of eachflank 11.4, i.e. the width of each flank 11.4.

In use, the inner shaft 11 and the outer shaft 9 transmit torque fromone to the other. The torque is transmitted thanks to the contactbetween the outer surfaces of the flanks 11.4 of the inner shaft or tube11 and the inner surfaces of flanks 9.2 of the longitudinal projections9.1 of the outer shaft or tube 9, i.e. the inner surfaces oflongitudinal grooves of the outer shaft 9 corresponding to thelongitudinal projections 9.1.

Given the same torque transmitted and the same penetration degreebetween the inner shaft 11 and the outer shaft 9, a pressure isgenerated between the surfaces of mutual contact, which the lower is,the greater the width G of each flank 11.4 and the corresponding flank9.2 is. Moreover, the more distant the contact surface is with respectto the axis of the telescopic shaft 3, the lower the pressure is. InFIG. 29 letter B indicates the distance of the median point of the flank11.4 from the axis A-A of the telescopic shaft 3.

In order to reduce the pressure between the mutual contact surfaces ofthe shafts or tubes 9 and 11, it is advantageous to make the profiles ofthe inner shaft 11 and of the outer shaft 9 so that the ratio betweenthe flank width G and the distance B of the flank median point from theaxis of the telescopic shaft 3 is at least equal to, or greater than,approximately 0.35, preferably equal to, or greater than, approximately0.45, preferably equal to, or greater than, approximately 0.5, andpreferably equal to, or lower than, approximately 0.8, preferably equalto, or lower than, approximately 0.6.

According to some embodiments, the product of the flank width G and thedistance B of the flank median point from the axis of the telescopicshaft 3, divided by the maximal diameter Dmax of the inner shaft 11, isequal to, or greater than, approximately 2. The maximal diameter Dmax ofthe inner shaft 11 is the diameter measured at the head surfaces 11.3 ofthe longitudinal projections 11.1.

In other words, it has been found that particularly advantageousoperating conditions, in terms of mechanical stress reduction, togetherwith an adequate compromise in terms of dimensions and weight of thecomponents 9 and 11 of the telescopic shaft occur if

$\frac{B*G}{D\max} \geq 2$

The value of this ratio is preferably comprised between approximately 2and approximately 5, and more preferably between approximately 2.1 andapproximately 4.5 mm. These values are obviously calculated by using thesame unit of measurement for B, G and Dmax. The ratio is notdimensionless; it is expressed in the unit of measurement of the lengthused for the three measurements involved. If the measures are expressedin millimeters, the value of the ratio indicated above is also expressedin millimeter. The above relationship is valid for lengths measured inmillimeters.

The thickness S11 of the wall of the inner shaft 11 is advantageouslycomprised between approximately 2 mm and approximately 8 mm, andpreferably between approximately 3 mm and approximately 6 mm. In theintervals above, the actual values are set during designing, based onthe maximal torque to be transmitted.

The shape of the cross-section of the outer shaft 9 is complementary tothat of the inner shaft 11, and it is therefore defined by the aboveratio. The thickness S9 of the wall of the outer shaft 9 may be of thesame order of magnitude of the thickness S11.

1. A universal joint comprising: a first fork comprising a first sleevewith a first longitudinal axis, a first member for connecting to a firstshaft, and a first pair of arms diametrically opposite to each otherwith respect to said first longitudinal axis and extending in adirection opposite the first sleeve, a second fork comprising a secondsleeve with a second longitudinal axis, a second member for connectingto a second shaft, and a second pair of arms diametrically opposite toeach other with respect to said second longitudinal axis and extendingin a direction opposite the second sleeve, a spider comprising: a firstpair of trunnions coaxial with each other and inserted into a first pairof aligned and opposite seats provided in the first pair of arms, and asecond pair of trunnions coaxial with each other, orthogonal to thefirst pair of trunnions, and inserted into a second pair of aligned andopposite seats provided in the second pair of arms; wherein a respectiveneedle bearing is provided between each trunnion and the respectiveseat; wherein: the first sleeve is connected to the first pair of armsthrough a first collar extending from the first sleeve and having aconcave shape and an end edge, from which the first pair of armsextends; and the second sleeve is connected to the second pair of armsthrough a second collar extending from the second sleeve and having aconcave shape and an end edge, from which the second pair of armsextends; and each collar has an inner concave surface of substantiallyspherical shape, with a center located on an axis of the respectivealigned pair of seats of the respective pair of arms.
 2. The universaljoint according to claim 1, wherein the first sleeve, the first collarand the first pair of arms are made in a single piece; and wherein thesecond sleeve, the second collar and the second pair of arms are made ina single piece.
 3. The universal joint according to claim 1, whereineach of said first collar and second collar is cup shaped flared fromthe respective first sleeve and second sleeve towards the edge, fromwhich the respective first pair of arms and second pair of arms extends;wherein the first collar surrounds a first hollow space and the secondcollar surrounds a second hollow space.
 4. The universal joint accordingto claim 1, wherein each of said first collar and second collarcomprises a concave inner surface.
 5. The universal joint according toclaim 4, wherein the concave inner surface delimits a concave space, theheight whereof, measured in the direction of the longitudinal axis ofthe respective sleeve, is equal to at least approximately 10% of alength of the arms of the pair of arms extending from the edge of therespective collar.
 6. The universal joint according to claim 5, whereina height of the hollow space, measured in wherein a direction of thelongitudinal axis of the respective fork, is not greater thanapproximately 50% of the length of the arms of the pair of armsextending from the edge of the respective collar.
 7. The universal jointaccording to claim 5, wherein the height of the hollow space iscomprised between approximately 30% and approximately 60% of a diameterof the seats provided in the respective arms.
 8. The universal jointaccording to claim 1, wherein a ratio between a diameter of each seatprovided in the respective arm and a distance between the center of theseat and the edge of the collar is comprised between approximately 0.7and approximately 1.1.
 9. The universal joint according to claim 1,wherein one of said first sleeve and second sleeve comprises: an annularbearing surface adapted to support an outer accident-preventingprotection; an annular groove, axially spaced from the annular bearingsurface, adapted to engage an annular sliding block of theaccident-preventing protection; and wherein between the annular bearingsurface and the annular groove a respective coupling member for couplingto the respective shaft is located.
 10. The universal joint according toclaim 1, wherein dimensions of the collar, of the spider and of the armsare such as to allow a maximum inclination between the longitudinal axisof the first fork and the longitudinal axis of the second fork comprisedbetween approximately 60° and approximately 80°.
 11. The universal jointaccording to claim 1, wherein at least one of said sleeves is providedwith a protective lid closing an inner axial cavity adapted to receive arespective shaft.
 12. (canceled)
 13. The universal joint according toclaim 1, wherein a ratio between the diameter of each seat and a radiusof the inner concave surface of the collar is comprised between about0.48 and about 0.65.
 14. The universal joint according to claim 1,wherein a ratio between a length of needles of each needle bearing and adiameter of the respective trunnion of the spider is lower thanapproximately 0.56, wherein the needles have a diameter comprisedbetween approximately 2.2 and approximately 3.2 mm; and wherein thespider comprises a lubricating grease reservoir comprising a pair ofthrough holes, each of which extends from an end to the other of a pairof trunnions that are axially aligned with each other along one of axesof the spider.
 15. The universal joint according to claim 14, wherein aratio between the length of the needles and the diameter of therespective trunnion of the spider is greater than approximately 0.2. 16.The universal joint according to claim 14, wherein a ratio between thelength of the needles of each needle bearing expressed in millimeters,and the number of needles in each bearing is equal to, or lower than,approximately 0.39; and wherein the ratio between the length of eachneedle and the number of needles in each bearing is equal to, or greaterthan, approximately 0.18.
 17. The universal joint according to claim 14,wherein: each needle bearing comprises a cup-shaped cylindrical housingcoaxial with the respective trunnion of the spider; the needles arehoused between an outer cylindrical surface of the trunnion and an innercylindrical surface of the housing, and between a bottom surface of thehousing and a head surface of the respective trunnion an annular spaceris provided, interposed between the needles and the bottom surface ofthe housing.
 18. The universal joint according to claim 17, wherein thespacer is made of polymeric material.
 19. A power transmittingtelescopic drive shaft comprising: an outer tubular shaft; an innershaft, slidably housed in the outer tubular shaft; wherein the outertubular shaft and the inner shaft are torsionally coupled to each otherto transmit a torque and slidable coupled to each other in axialdirection; a first universal joint according to, applied to an end ofthe inner shaft; and a second universal joint according to, applied toan end of the outer tubular shaft, wherein the first universal joint andthe second universal joint each comprise the universal joint accordingto claim 1.